The present invention relates to emulsifier-free, stabilized lotions.
Lotions are important cosmetic and health formulations, and are common vehicles for delivery of topical skin treatments. Such lotions, which are generally oil-in-water or water-in-oil emulsions, are perceived as convenient, easy to apply and perhaps elegant. They have a pleasant texture, and allow the simultaneous application of water-soluble and oil-soluble ingredients. (Hereinafter the terms "lotion" and "lotions" will be understood generally to encompass personal care cosmetic, health and medical lotions, creams, ointments and the like.)
One consideration in the formulation of lotions containing a mixture of dissimilar liquids is the likelihood of separation of the liquids. Highly emulsified liquids are in a high energy state, i.e., there is a high level of interfacial energy between the molecules of dissimilar liquids. In such mixtures, droplets of like liquid are attracted and are inclined to coalesce and the more bouyant of the mixed liquids is inclined to separate from the other liquid and to rise to the surface of the mixture. Hence, emulsions are inherently unstable and tend to separate, i.e., they tend to seek their low energy state.
In order to achieve adequate shelf-life, cosmetic lotions typically require ingredients, called emulsifiers, to stabilize the emulsion in its otherwise high energy state. Such emulsifiers reduce interfacial energy, making the emulsion less unstable. They may also impede droplet-to-droplet contact and thereby inhibit coalescence.
Emulsifiers serve an essential purpose in a lotion, but are undesirable in topical applications, since they tend to cause skin irritation. Many emulsifying agents are demonstrably irritating: sodium lauryl sulfate, perhaps the most common emulsifier, is employed as a standard irritant in human skin tests. Modern product lotions tend to use less irritating nonionic emulsifiers, but the complete elimination of dermatologically questionable ingredients such as emulsifiers is an increasingly important goal in the formulation of topical lotions.
A generic method for elimination of chemical emulsifiers would be an important step in the campaign against use of irritants. One alternative to the use of chemical emulsifiers might include solidifying the suspended droplets so they cannot merge or circulate. However, any physical method of emulsion stabilization must remain effective over a wide range of liquid surface tensions, densities and viscosities, given the wide range of ingredients compounded into lotions. Furthermore, the end product should be a soft lotion, rather than a gritty slurry, and one which does not leave a visible residue on the skin.
It is therefore an object of the present invention to provide an emulsifier-free stabilized lotion.
It is another object of the present invention to provide an emulsifier-free stabilized lotion which is perceived as a soft emulsion, rather than as a gritty slurry, and does not leave a visible residue on the skin.